1. Field of the Invention
The present invention relates to an intraventricular multielectrode catheter for mapping the activation sequence of a ventricle of a heart in order to locate ectopic foci (regions of abnormal electrical activity), which cause ventricular arrhythmia, and, in particular to a catheter which, in an expanded condition, has a shape approaching the shape of the ventricle.
2. Description of the Prior Art
Intraventricular mapping is a technique which permits spatial recording of electrical activity of a ventricle as a function of time in an endocardial manner, which can be done on a physiological condition (a condition of normal functioning of the heart). The information obtained by mapping is used for analysis of the activation sequence and the wave form, the potential distribution and, in particular, for localization of the ectopic foci during the depolarization and the repolarization.
A number of devices for the intraventricular mapping, which have multiple electrodes and can be inserted into the ventricle through the blood vessels, are known. Examples of such devices are disclosed in the following U.S. Pat. Nos. 3,326,207 (Egan), 3,825,015 (Berkovits), 3,903,897 (Woolons), 3,995,623 (Blake), 4,172,451 (Kline), 4,699,147 (Chilson), 5,215,103 (Desai).
Of these patents, only the Chilson patent discloses a catheter which, in an expanded condition, has a shape that can approaches the shape of the ventricle. Chilson discloses a catheter which consists of an outer flexible tubing, having an open proximal end and a distal end and four elongate wire assemblies which are received in the outer tubing and has six leads on the distal end of each wire assembly.
When the catheter is inserted into the ventricle, the wire assemblies expand to form an elliptical envelope. Upon expansion, the leads on the wire assemblies make contact with the endocardium to effect mapping. The Chilson device however, has a number of drawbacks. First, Chilson shows an elliptical envelope, formed by the wire assemblies in the expanded condition and which does not correspond to the cone shape of the ventricle. Since the envelope should form within only the ventricle (otherwise, it may compromise the cardiac function and damage the valve of the aorta by dilating the structure), only about half of the leads (that is 12 leads) can make contact with the endocardium. Considering the irregularity of the surface of the endocardium, the number of the leads making contact with the endocardium is even less than twelve, which is not enough for the mapping. Second, there is no mechanism in the Chilson catheter for absorbing the change in the ventricular volume during the contraction of the heart. Therefore, the contraction of the heart will cause the leads to change their position and even to lose their contact with the endocardium so that the measurement will be less reliable if at all possible. Third, Chilson's proposal to rotate the elliptical envelope to measure the electrical activity of the ventricle is practically impossible and potentially harmful because tendons and papillary muscles in the ventricles prevent such movement and the movement may also damage those structures. Also, the mapping is a spatial representation of the electrical activity as a function of time. When the electrical activity of the ventricle is measured in a different cardiac cycle by rotating the elliptical envelope, the time resolution of the measurement becomes less reliable.
Accordingly, a main object of the present invention is to provide a catheter which would overcome the above-discussed drawbacks.
Another object of the invention is to provide a catheter which, in an expanded condition, would have a shape substantially corresponding to the shape of the ventricle.
Yet another object of the invention is to provide a catheter which is able to absorb the change in the heart volume when the heart contracts.
Still another object of the invention is to provide a catheter having 100 or more leads to insure an accurate mapping.
A further object to the invention is to provide a catheter whose leads make contact with the entire surface of the endocardium.
Furthermore, an object of the invention is to provide a catheter whose leads make good contacts with the endocardium as during the contraction so during the relaxation of the heart, which requires that the catheter changes its shape to accommodate the change in the volume of the ventricle.
Additionally, an object of the invention is to provide a catheter which does not compromise the cardiac function when performing the intraventricular mapping under the physiological condition when being introduced into the ventricle.